Volume 11 (2017) Pages 1-9
Graminaceous plants biosynthesize siderophores and secrete it into the rhizosphere, solubilize insoluble Fe(III) by chelation, and take up the Fe(III)-siderophore complex. Active uptake of Fe(III) in microorganisms such as Pseudomonas fluorescens is also based on siderophores. However, vegetative plants including the tomato, cannot synthesize siderophores and take up Fe(III) directly. The growth of tomatoes under Fe(II)-deficient conditions supplemented with the Fe(III)-siderophore complex is enhanced in comparison with the growth of the control. However, the mechanism of iron absorption has not been clarified yet.Two-week-old seedlings were transferred to a liquid medium inoculated with P. fluorescens. After incubating for four days, the iron concentration of plants increased compared with that of non-symbiotic seedlings. Moreover, the expression of the Fe(II) transporter IRT1 and Nramp3 was analyzed by qRT-PCR. The expression of IRT1 was not induced until day 7 but that of Nramp3 was induced in four days. In addition, Fe(III) chelate reductase (FRO) activity was high in symbiotic seedlings after four days. These results suggest that the chelated Fe(III) was reduced to Fe(II) by FRO and taken up by Nramp3. Siderophore-mediated Fe(III) uptake by tomato is believed to be a useful strategy for increasing iron uptake from the environment.